Javascript race condition?

Question

var len1 = $("div").length
// can a new div inserted here?
var len2 = $("div").length
console.log(len1 === len2) // always true?

Is it possible for some rogue script to insert a new div between jQuery calls?

As long as both `length` calls happen in the same function: no. JS is single threaded (for the most part), so no other function can insert another div in between. — Sirko, May 19 '15 at 07:59
This might be of interest to you: http://stackoverflow.com/a/8996894/551093 — Christian, May 19 '15 at 08:00
http://jsfiddle.net/arunpjohny/qqo54zr8/1/ - if a new element is inserted to the dom between those 2 statements the length will be refresed — Arun P Johny, May 19 '15 at 08:01
@ArunPJohny: Pretty sure that's not what he meant, but I like the way you think :) — Amadan, May 19 '15 at 08:02
But, no... nobody else will be able to insert anything between the given 2 statements — Arun P Johny, May 19 '15 at 08:03

score 2 · Accepted Answer · edited May 23 '17 at 12:14

Short answer: No.

Longer answer: You don't seem to be using alert or confirm in your code, and so the couple of weird edge cases in Firefox (which may only be in older versions) related to alert and confirm don't come into play. This answer from 2010 goes into those in detail.

But no, barring the above, no JavaScript code that accesses the DOM can be run between one statement and another in your code. Browsers run JavaScript with a single UI thread (and zero or more web worker threads, but web worker threads can't access the DOM).

Javascript race condition?

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